Extensive efforts have been made thus far to develop some catalytically active multinuclar metal complexes in our group. In this context, multinuclar coordination compounds involved in the active centers of the so-called metalloenzymes must be viewed as related to many of our research projects. Apart from the relatively abundant transition metals often found in the active centers of the enzyms, we have been focusing the studies on complexes with heavier or precious metals, such as Pt, Rh, and Ru. Our recent studies involve the following topics:●Syntheses of multinuclear metal complexes with unusual electronic structures, such as strong metal-metal interactions leading to unusual/amzing reactivities.●Development of Photosynthetic molecular devices which generate molecular hydrogen from water upon irradiation of visible light, which may be replaced with soloar light.●Studies on the solution properties of metal complexes, which give better understanding to the reacction mechanisms of them in their catalysis.●Syntheses, X-ray structure analysis, and physical properties of one-dimensional platinum chain complexes, where the anisotropic properties, nonlinear optical properties, metallic conduction properties, solid-satate emission properties, sensor properties (such as vapochromic behaviors upon exposure to a certain solvent gas) are focused.●Development of molecular sensor by use of metal center as the recognition site for the sensing.For instance, we are now interested in the development of hydrogen-sensing metal complexes.

Here students learn how to synthesize the coordination compounds including those of the ligands to be used. They also have a variety of chances to learn how to characterize, how to measure, how to calculate, how to evaluate, and so on. A large variety of analytical techniques must be used to perform the research on coordination chemistry. Thus, we think we are analytical chemists at the same time.

Studies of New Homogeneous Catalysts based on Coordination Compounds towards the Water Cleavage into Molecular Hydrogen and Oxygenkeyword : the Water Cleavage into Molecular Hydrogen and Oxygen1991.04.

Current and Past Project

Studies on the reaction mechanism and the structure-activity relationship in the single-molecule photo-hydrogen-evolving molecular devices consisting of ruthenium and platinum centers

Ken Sakai, Hybrid Molecular Catalysts and Photocatalysts for Solar Water SplittingReactions, 3rd Japan - UK Joint Symposium on Coordination Chemistry, 2018.04, [URL], The chemistry of water oxidation and reduction has been extensively studied from manyviewpoints due to their significant relevance to solve the problems arising from the globalwarming and the shortage of fossil fuels. For both processes, proton-coupled electrontransfer (PCET) processes have been considered to play the central role in drasticallylowering the activation barriers for the relevant elementally steps. In the past decades, ourgroup has paid specific interest in clarifying the mechanisms of transition-metal-basedmolecular catalysis for both processes [1-6]. In this presentation, some PCET processes thatgovern the rate of catalytic water reduction to evolve dihydrogen from water are discussed.The figure shown below illustrates that transition-metal-catalyzed water reduction can beroughly considered to undergo through three different types of PCET-based ratedeterminingsteps. The first metal-centered model is the case where the anti-bonding orbitalin the square planar complex like a Pt(II) system forms a hydridoplatinum(III) intermediate[1,2,5]. This path will was also shown to undergo via formation of a diplatinum(II,III)interemediate due to its favorable stabilization via the Pt-Pt bond formation. An exceptionalcase is a Co NHC catalyst, for which metal-centered PCET occurs upon reduction of Co(II)d7leading to protonation at a Co(I) d8system [4], implying that the dz2 filled orbitalprovides basicity strong enough to promote protonation at the metal center. Our recentstudies also demonstrated some unique hydride forming paths in which ligand-basedreductions coupled with protonation at the ligand geometries can lead to metal hydrideintermediate species required to catalyze hydrogen evolution from water [5,6].References1. Sakai, K.; Ozawa, H., Coord. Chem. Rev., 2007, 251, 2753.2. Ogawa, M. Ajayakumar, G.; Masaoka, S.; Kraatz, H.-B.; Sakai, K., Chem. Eur. J., 2011,17, 1148.3. Kimoto, A.; Yamauchi, K.; Yoshida, M.; Masaoka, S.; Sakai, K., Chem. Commun., 2012,48, 239.4. Kawano, K.; Yamauchi, K.; Sakai, K., Chem. Commun., 2014, 50, 9872.5. Yamauchi, K.; Sakai, K., Dalton Trans., 2015, 44, 8685.6. Koshiba, K.; Yamauchi, K.; Sakai, K., Angew. Chem. Int. Ed., 2017, 56, 424.

5.

Ken Sakai, Molecular Design and Control of Transition Metal Complexes and Their Hybrids for Photocatalytic Water Oxidation and Reduction, The 2018 Gordon Research Conference, 2018.01.